Silane reagents are used in the preparation of composite materials and for introducing or immobilizing suitable functional groups on silica and other inorganic materials. These inorganic materials, such as silica gel, porous glass, alumina, or titanium dioxide, when modified with organosilicon compounds that introduce various organic functional groups onto their surface, are useful in many technical fields, such as liquid chromatography, immobilization of enzymes, heterogeneous catalysis, and the preparation of filled polymers or laminates. See, K. K. Unger, Porous Silica, Elsevier (New York: 1979).
Silane reagents with chelating functional groups, such as reagents of 8-hydroxyquinoline and ethylenediamine, are known and described in the literature, e.g., E. P. Plueddemann, Silane Coupling Agents, Plenum Press (New York: 1980). Some of these reagents are used commercially.
Efficient and commercially successful silane reagents containing a complexon group based on ethylenediaminetetraacetic acid (EDTA) or diethylene triamine pentaacetic acid (DTPA) have been heretofore unknown. The closest known reagents are those containing iminodiacetic acid as the functional chelating group. see Chromatographia, Vol. 17, 200 (1983).
Iminodiacetic silane reagents of the formula EQU (R.sup.1 O).sub.3 SiCH.sub.2 CH.sub.2 CH.sub.2 (NRCH.sub.2 CH.sub.2).sub.n NH.sub.2-m R.sub.m
are known, where R.sup.1 is methyl or ethyl, R is H or CH.sub.2 COOH, M is H or alkaline metal, n is 0 or 1, and m is 1 or 2. See, U.S. Pat. No. 4,071,546. These reagents are prepared by carboxymethylation of the corresponding amine with sodium chloroacetate in aqueous medium.
The main disadvantage of these known reagents is their low chelating ability, caused by the low number of donor sites in the iminodiacetic acid derivatives and by incomplete carboxymethylation in the ethylenediamine derivatives.
There are also serious disadvantages associated with the preparation of the known reagents. The synthesis of iminodiacetic acid reagents comprises several relatively complex steps. The ethylenediamine derivatives are not chemically homogeneous. In both cases, carboxymethylation of the amino groups is carried out in an aqueous medium, which results in the uncontrolled hydrolysis of alkoxy groups with the formation of silanols, which then spontaneously condense into siloxane oligomers.
Attempts to produce silane reagents and modified inorganic materials incorporating the more powerful chelating derivatives of EDTA and DTPA have not been very successful. A suitable complexon compound modified with alkoxysilyl or chlorosilyl, thereby enabling simple and efficient production and processing, has eluded discovery. Preparation of suitable EDTA or DTPA derivatives of inorganic materials via 3-aminopropyl or 3-glycidyloxypropyl derivatives has also been unsuccessful, primarily because the polymeranalogous reaction is very slow, does not proceed quantitatively, the resulting material surface is considerably heterogeneous with respect to functional interactions, and only a low chelation capacity is achieved.
Known polymeric complexons containing EDTA or DTPA, as described for example in U.S. Pat. No. 4,343,920, are also unsuitable. These materials swell, and have a low mechanical stability. In addition, the functional chelating group frequently appears within the material and not only on the surface. As a result, equilibrium in the chelation of cations is achieved slowly.